The number of $1M tax filers in Massachusetts is on the rise; See the latest town-by-town data here

The number of Massachusetts tax filers claiming $1 million or more in adjusted gross income doubled from 2004 to 2015, with more than 18,000 filers hitting that threshold in the latest data released by the state's Department of Revenue.

That increase comes as voters in the November election may consider a ballot question on whether the state should impose a 4 percent increase in the tax rate on income over $1 million. Business groups have mounted a legal challenge to the so-called "Millionaire tax," and the state's Supreme Judicial Court is expected to issue a ruling on whether the question is constitutional.

On the slides that follow, we'll take a look at the data in a few ways: Which communities have the most $1 million filers? Which have the most per capita? And, in which communities did these filers report the highest average adjusted gross income?

But first, let's talk about some blind spots in the data.

Like all datasets, the Department of Revenue's spreadsheet on tax filers reporting $1 million or more in adjusted gross income tells a story -- but it doesn't tell the whole story. So before we get going, a few notes:

The dataset reflects a point in time -- not annual income.
The state's figures include filers' average adjusted gross income for 2015 only. That doesn't offer a window into how many of those filers typically earn more than $1 million in a year, or how many hit the $1 million mark only through a one-time event like the sale of a business or other major asset.

People who didn't file in Massachusetts aren't counted.
While the maps below show the number of filers in 194 Massachusetts communities, there are still more people at that income level with homes here -- but who claim their primary residence in another state.

We're talking about adjusted gross income.
That's different, of course, from take-home pay. After taxes, the net income of some of the filers included in this dataset may be well below $1 million.

The state excludes "small towns" with five or fewer filers.
The raw data offers aggregate figures for 158 "small towns," including Devens, which is a Census Designated Place. There were 307 $1 million filers in those 158 communities, with an average adjusted gross income of $2.275 million.

The dataset doesn't include all sorts of other interesting variables.
The Department of Revenue spreadsheet includes:

number of $1 million filers per community;

the total adjusted gross income of those filers;

average adjusted gross income per filer;

total after-credit taxes paid;

and average tax paid per filer.

Using those existing variables, I've also calculated each community's number of $1 million filers per 1,000 residents. But there are other relationships we could explore, such as data on property tax rates or median household income.

Have an idea for a way to mash-up this dataset with another? Post your suggestions to the comments.

Next, here's a chart with all of the income data.

Use the check boxes at the right to choose which variables to view, or to select a specific community or communities.

Graphics and maps by Greg Saulmon / The Republican

Number of filers: The raw totals

In the map below, click or tap a community to see the number of filers claiming $1 million or more in adjusted gross income in 2015.

The slides that follow show the 10 communities with the most $1 million filers.